[PATCH v2 3/3] tty: serial: omap-serial: wakeup latency constraint is in microseconds, not milliseconds

[Govindraj]

On Thu, Jan 26, 2012 at 8:20 AM, Paul Walmsley <paul at pwsan.com> wrote:
> The receive FIFO wakeup latency estimate in the omap-serial driver is
> three orders of magnitude too small.  This effectively prevents the
> MPU from going to a low-power state when CONFIG_CPU_IDLE=y.  This is a
> major power management regression and masks some other FIFO-related
> bugs in the driver.
>
> Fix by correcting the most egregious problem in the RX wakeup latency
> estimate.  There are several other flaws in the estimator; these will
> be fixed by a separate patch series intended for 3.4.
>
> The difference in low-power states with this patch can be observed via
> debugfs in pm_debug/count.
>
> This estimate does not have any effect when CONFIG_CPU_IDLE=n.
>
> Signed-off-by: Paul Walmsley <paul at pwsan.com>
> Cc: Kevin Hilman <khilman at ti.com>
> Cc: Govindraj.R <govindraj.raja at ti.com>
> Cc: Tomi Valkeinen <tomi.valkeinen at ti.com>
> Cc: Alan Cox <alan at linux.intel.com>
> Cc: Greg Kroah-Hartman <gregkh at suse.de>

Acked-by: Govindraj.R <govindraj.raja at ti.com>

> ---
>  drivers/tty/serial/omap-serial.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> index 11fa156..72fa783 100644
> --- a/drivers/tty/serial/omap-serial.c
> +++ b/drivers/tty/serial/omap-serial.c
> @@ -740,8 +740,7 @@ serial_omap_set_termios(struct uart_port *port, struct ktermios *termios,
>        quot = serial_omap_get_divisor(port, baud);
>
>        /* calculate wakeup latency constraint */
> -       up->calc_latency = (1000000 * up->port.fifosize) /
> -                               (1000 * baud / 8);
> +       up->calc_latency = (USEC_PER_SEC * up->port.fifosize) / (baud / 8);
>        up->latency = up->calc_latency;
>        schedule_work(&up->qos_work);
>
>
>
> --
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